Studies confirm what you've noticed. Patients with early signs of carpal tunnel syndrome (CTS) often report hand weakness and clumsiness. Yet when grip and pinch strength are measured, they seem normal.

The nerve to the thumb (median nerve) is affected by CTS. The effects may be different than expected. For example, according to a recent study at the Hand Research Lab in Pittsburgh, it looks like the other nerves help take over for the damaged median nerve.

Grip and pinch strength are also movements accomplished using several muscles. The other muscles may kick in giving a "normal" strength reading. But when it comes to a fine motor task such as picking something up, the impaired coordination of sensory and motor messages make the task difficult if not impossible.

Scientists don't have the complete answer to your question. For now we can validate your experience and say more studies are underway to find an explanation.